Recovery of high purity indene by chromatographic fractionation and fractional distillation



United States Patent M RECOVERY OF HIGH PURITY INDENE BY CHRO- MATOGRAPHIC FRACTIONATION AND FRAC- TIONAL DISTILLATION Application November 29, 1955 Serial No. 549,876

7 Claims. (Cl. 260-674) No Drawing.

This invention relates to a process for recovering high purity indene by chromatographic fractionation and fractional distillation. More particularly, it relate to the recovery of high purity indene by multiple successive chromatographic fractionation followed by fractional distillation.

Indene is found in the tars from coal, lignite and the like and is also manufactured by passing tetrahydro-naphtha lene over silica-alumina catalysts at high temperatures, for example, about 670 C. The commonest source is from coal tar naphthas. Substantially all of the indene in the coal tar may be concentrated in a naphtha fraction boiling in the range of about 160? to about 200 C. The indene content of such fractions may vary substantially depending in part upon the source of the naphtha and in part upon the sharpness of the cut but usually ranges from about 35% to about 70% by volume. It is possible to produce a fraction containing abouts75% of indene by fractional distillation but such a fraction contains only about 20% of the indene present in the tar. This represents an undue loss of valuable components and hence it is desirable to devise methods whereby indene of greater purity and representing a higher proportion of that available can be produced.

Indene-containing naphtha fractions. falling within the aforementioned boiling range contain a variety of rather close boiling components which make it impractical or impossible to produce indene in the degree of purity desired. One of the major uses of indene is in the production of resins such as the .coumarone-indene resins which are widely used for coatings and other purposes. The production on a commercial scale of high purity indene would make possible the production of valuable derivatives of indene which is not now practical because of the present inavailability of high purity indene in commercial quantities.

We have devised a method whereby a greater proportion of available indene of higher purity can be produced than was heretofore possible, at least on a practical scale.

In a copending application entitled Chromatographic. Separation of Indene, Serial No. 549,877,-filed concur-- rently herewith, we have described a method comprising subjecting indene containing naphtha to a chromatographic fractionation over a suitableadsorbent such as silica gel, activated alumina, activated carbon and the like to obtain a fraction rich in indene. Thereafter, the said fraction may be subjected to a second chromatographic fractionation to produce a further purification, and the second said fraction may be'subjected to a further chromatographic fractionation to produce a product of high indene content which represents a high recovery of available indene originally present in the naphtha.

We have discovered that if naphtha fractions which 2,939,821 Patented Mar. 29, 1960 2 have been subjected to chromatographic fractionation are fractionally distilled, high percentages of the indene originally present can be obtained a a substantially pure product. In addition, high purity products such as methyl benzenes, indane, coumarone, methyl-coumarone, benzonitrile and pyridines such as methyl-pyridines can be obtained.

Among the adsorbents which may be used, activated silica gel is preferred. Activated alumina is useful although not entirely equivalent to activated silica gel. Various grades of activated carbon of the adsorbent variety may also be employed.

While the operation is normally carried out by percolating the naphtha through a fixed bed of the adsorbent, various continuous methods may also be employed.

The invention will be described in connection with the use of silica'gel but it .will be evident as to how other suitable adsorbents may be used in place thereof. It will also be described in connection with a fixed bed operanon.

The adsorbent may be of any suitable mesh size, for example, 10 to 200 mesh or finer. It is usually packed evenly in a vertical column of suitable dimensions to obviate channeling. In order to facilitate the wetting of the adsorbent by the naphtha, petroleum ether (B.P. Bil-60 C.), or other low boiling saturated hydrocarbon which is readily displaceable from the adsorbent by the naphtha components, is passed through the column until n the naphtha.

The indene-containing naphtha which has been previously fractionated to the desired boiling range and which preferably contains the major portion of the indene present in the coal tar, is passed through the column. It is preferred that the boiling range of the naphtha be as narrow as possible, consistent with the maximum recovery of indene from the tar. Usually this is Within the range of to or 200 C. The naphtha constituents, being much more readily adsorbed than the petroleum ether, displaces it so that the first material through the column is the petroleum ether with which the bed was originally wetted. The petroleum ether can be recovered as a separate fraction and purified if desired by fractional distillation since its boiling range is far below that of the naphtha. The course of the fractionation i conveniently followed by determining the refractive index of the material coming through the column. of'course, be used.

The naphtha is passed through the column and when the refractive index of the eflluent reaches a predetermined value, the flow, is stopped. The remaining material is eluted or desorbed, for example with another organic liquid which is preferentially adsorbed and hence disa places the adsorbed components of the naphtha. The eluting liquid is chosen so as to be readily recoveredfor example by solvent extraction or by distillation. A low ture and enhance its eluting poweix, Carbon tetrachloride or otherhalogenated hydrocarbon boiling in a dif ferent range from the naphtha may be employed, as may dioxane, nitrobenzene, etc. Steam may he used, pe il?- ularly to remove the eluting or d'esorbing agent liquids n from the adsorbent.

Alternatively, more than one eluent may be employed. s For example benzene may be used first, followed by Other methods could,

ethanol. The naphtha contains certain non-hydrocarbons such as coumarone, methyl coumarone, methyl pyridines and benzonitrile which are strongly adsorbed and not readily displaceable by non-polar eluents. By following this procedure these can be readily recovered and separated by, for example, fractional distillation.

As the eluting liquid passes downward through the column the adsorbed components of the naphtha are displaced.

The first components leaving the column are largely saturated hydrocarbons having the lowest refractive index. This is followed by fractions predominantly cyclic, first naphthenics and then aromatics which are largely trimethyl benzenes, which latter fraction contains indane if it is present. The first fractions contain little or no indene. There is a gradual increase in indene content. When the refractive index reaches a value of about 1.49 an intermediate fraction is usually recovered containing between 30% and 40% indene. This fraction contains indane if it is present. The fraction may be reprocessed separately or in combination with the naphtha charge to recover additional indene. The indene content of subsequent fractions gradually increases. It is possible to recover about 20% of the indene content of a naphtha (40% indene content) of about 80% purity by a single chromatographic treatment. Over 50% can be recovered of 76% purity in the same way. By subjecting the indene-rich fraction to fractional distillation in a high eificiency column having say 50 to 100 theoretical plates, 60% of the indene in the naphtha can be recovered having 95% or greater purity. By contrast only 20% of the indene of 75% purity can be recovered by fractional distillation alone.

An undistilled high indene-content fraction from the first chromatographic fractionation, for example, the 76% fraction just referred to or a fraction containing 60-70% indene and representing a correspondingly larger proportion of the original naphtha, may be subjected to a second chromatogram.

By this means more than 20% of the original indene content can be recovered at 88% purity, or more than 40% of 80% purity. Fractional distillation of a rich fraction from the second chromatographic treatment yields substantially pure indene.

The rich fraction from the second chromatogram may be subjected to a third chromatogram, and in this way 65% of the original indene content of 85% purity can be obtained. About 25% of the original indene content can be recovered having about 90% or more purity. The refractive indices of the cuts making up this fraction range from about 1.552 to about 1.569. The rich fraction from the third chromatogram is fractionally distilled and yields practically pure indene amounting to.

60% or more of the indene in the original naphtha.

The final or bottoms fraction from each of the chromatograms contain substantial quantities of non-hydrocarbons. These are best displaced from the adsorbent by eluents such as a lower alcohol or a halogenated hydrocarbon. Such fractions may be subjected to a separate chromatographic fractionation. A small fraction, apparently largely composed of methyl pyridines, was the first to be separated. The major portion of the bottoms, representing about 70-80% is next obtained. This can be fractionally distilled to recover as separate products, cournarone, indene and methyl-coumarone in amounts which vary depending on the naphtha. Upon distilling such a fraction from a representative coal tar naphtha.

the original naphtha were cournarone 2.2%, benzonitrile 1.3% and methylcoumarone 0.5%.

The amount of material passed into the column per unit weight of silica gel may vary considerably depending upon the subsequent steps to be employed, the percentage of indene in the naphtha, the nature of the non-indene components, and the degree of purity desired in the indene containing fraction. According to one embodiment the naphtha charge is stopped when the refractive index taken at 25 C. reaches about 1.500. The material which has come through the column at this point comprises a small amount of residual petroleum ether and most of the saturated hydrocarbons contained in the original naphtha. The eluting liquid is then charged to the column.

The next fraction recovered has a refractive index between 1.526 and about 1.540 and contains considerable amounts of indene of the order of 30% to 40%. If indane is present most of it appears in this fraction, the remainder is largely trimethyl benzenes. This material is collected separately and may be subjected to further chromatographic separation. In this way additional concentration of the indene and further recovery can be had of that available.

Alternatively, the intermediate fraction may be fractionally distilled to remove a major portion of the methyl benzenes and to recover indene of relatively high purity.

Material having a refractive index of about 1.541 to about 1.551 is recovered and is subjected to a second chromatographic fractionation conducted as previously described. The heart cut of this material is then recovered and this in turn is subjected to a third chromatographic fracitonation.

Depending upon where the heart cut is taken the bottoms fraction fromv each of the chromatograms may contain a high proportion of indene (up to, say 60%) in addition to other hydrocarbon and non-hydrocarbon components. Much of the indene from these fractions can be recovered by subjecting them, either separately or as a combined fraction, to chromatographic fractionation. This can be fractionally distilled to obtain substantially pure indene.

In a like manner, intermediate fractions taken just prior to the heart cut and containing 30-60% indene, can be reprocessed either separately or as a combined feed. The indene-rich fraction can be distilled to obtain substantially pure indene.

, The heart cuts from the chromatographic fractionation of either the intermediate or bottoms fractions can be recovered as such or either, or both can be added to the charge to the third chromatogram of the series conducted on the original naphtha. The indene rich-fraction of this step is distilled to obtain substantially pure indene.

While more than three separations can be used, there appears to be little to be gained as a practical matter.

The flow of eluent is continued until substantially no further naphtha components are found in it. This point is reached when the refractive index ofthe effluent is substantially the same as that of the eluent being used. Any naphtha components dissolved in the eluent can be recovered by fractional distillation.

The eluent may be displaced from the adsorbent by passing an inert gas therethrough usually at an elevated temperature of say -250" C. Steam is satisfactory although nitrogen or carbon dioxide, or low boiling hydrocarbons such as methane, ethane, propane,.butane, etc., may be used. It is preferred not to use an oxygen containing gas both because of fire hazard and because of the adverse effect of any adsorbed oxygen on the indene. After the eluent is removed, the adsorbent is cooled and is ready for reuse.

In carrying out the adsorption operation, whether one or moresteps are employed, a series of columns may be a step and a heating medium passed through during regeneration.

The operation is preferably carried out at room temperature, say 20-30" C. or below. Because of the heat of adsorption it is necessary to cool the column to pre ent the temperature from rising. In general, the fractionation is more eifective at low temperatures.

' In some instances, particularly when the indene content is high, say 75-90%, it is desirable to dilute the naphtha prior to contact with the adsorbent to about 40-60% indene concentration with a low boiling hydrocarbon such as pentane, hexane or the like, or with pe-- troleum ether. These appear in the first fractions through the column and can be recovered in a subsequent distillation step, or can be reused for dilution purposes.

The fractional distillation can be carried out in any eflicient apparatus wherein a close fractionation can be obtained. It may be carried out at atmospheric pressure or at reduced pressures. It may be either batch or continuous.

We are not certain as to why the improved effects are obtained in the process whereby such a large recovery of pure or substantially pure indene is accomplished. It is a fact that the individual constituents of the naphtha fraction boil close together. It is possible that some of these form constant boiling mixtures with other components, and that the chromatographic separation removes part of these so that the balance is upset, permitting sharp separation by distillation. We do not believe that such an effect could be anticipated from what has been taught in the prior art.

The following example shows results that were obtained by subjecting a typical coal tar naphtha to single and multiple successive chromatographic separation. Table I shows'the distillation characteristics of the fraction using a 25 plate column, a reflux ratio of 10:1 at 750 mm- Pres u e and at 00 mm. pre ur Table II shows physical and chemical constants of the naphtha fraction.

The naphtha fraction (350 grams) was passed through an eight foot column approximately mm. in diameter which was firmly packed with 2400 grams of minus 200 mesh activated silica gel which had been pre-wetted with petroleum ether. The results are shown in Table 'III.

TABLE III Chromatograpl zy of thecoal tar naphtha fraction over il ca l 7 Volume Bromine Indene, Fraction 11,," d4 RI 1 No. Percent ml. Percent A (PE) D1 1 Refractivity intercept (n,#% d4).

1 Petroleum ether.

Fractions D to D; were distilled in a 100-plate Pod-' bielniak column and fractionated at 100mm. pressure at a take-off rate of 30 ml./hr. The'result's are shown in Table IV.

7 TABLE IV 7 Fractional distillation of chromatographic fractions Boiling Volume Fraction Point, Vol., m d RI 6 Bromine Indene, 0. percent N 0. percent ml. percent 50.8 23. 1 1 5. 4 1. 5247 0. 9315 1. 0589 30. 5 31. 0 14. l 9. 4 l. 5502 0. 9699 1.0652 77 39 3 121. 7 55. 3 3,6. 8 1. 5666 0. 9853 1. 0739 126 85 Bottoms 16. 5 7. 5 5.0

Calculated to 760 mm.

Based on original coal tar naphtha fraction.

750mm. 100 mm.

Fraction r Vapor Wt. Vapor Wt.

Temp, Percent nu Temp, Percent 11,,"

1. 1 1. 4944 97-101 4. 3 l. 5000 2. 5 1. 5025 104 6. 2 1. 5085 18.7 1. 5158 107 13. 8 1. 5185 29. 9 1. 5327 109 13. 9 1. 5288 9. 6 1. 5475 111 10.6 1. 5390 8.2 1. 5526 112 4. 8 1. 5450 12. 7 1. 5562 113 11. 1 1. 5507 4. 5 1. 5561 114 15.6 1.5570 0.9 1. 5508 115 12.0 1.5584 0. 9 1. 5422 Residue 6. 1 1. 5410 1.9 1 5300 Residue eavy o 3.0 Resin 4.3 I

Total Recovery..... 98.2 98. 4

Fraction 3 accounted for 78% of the indene in the original naphtha and was of purity. The materialcharged to the fractional distillation step contained the bulk of the indene and this amounted to 70.9% by volume of the original naphtha.

A similar experiment was carried out with the exception that a higher reflux ratio was employed and in this ay a p od containing 5% inde an mountin for about 60% of the indene in the original, naphtha tract o was Qb n d- T e r fr c v ndex of this 5% purity fraction was 1.5710 and its-melting point was" minus 4.5" C.

EXAMPLE III 1200 grams of the above naphtha fraction were passed. I I through 6.5 kilograms of 200 mesh activated silica gel,

through the column had a refractive index substantial-ly that of pure benzene. A final elution was then made with 95% ethanol. The results of the chromatograms TABLE VIII shownm Tables v VI and demonstrate the Triple chromatogram of chromatographic fractions s1stency of the method.

VolJI-fercent I d 0- D 8116 TABLE v Out No. Vol, 11,, d1" RI $01;- m (51.1 Chromatographic fractionation of the coal tar naphtha Frac- 0:1 Percent fraction over silica gel mm m 2'? ii 15335 03 53 i??? it 1 1 0 8 G tN Percent an M1 g gi g 18 5.7 1.5521 0.9503 1 0740 72 u P399395 53 32'? 24 3 ii??? 8' 352 i332? 3i 0 Accum- 32 10.2 1.5084 0 9915 1 0727 85410 %.0 3-6535 Naphthenes .0 5. 19.5 24.5 149202 0.8037 1.0011 Refmtmty mtelcept' :8 2&2 g-32g Fractions B to B were composited representlng 65% 015 50:0 1 54900 019523 1: 0720 09 of the indene in the original naphtha and being of 85% 8:3 58:3 g: 582% 53 pur1ty. The combined fractions were fractionally dis- 7.0 90.8 1 55720 1.0184 1.0481 00 t1lled 1n the IOU-plate column at 100mm. pressure with a l012 ml./hr. takeoff. The results are shown in Table IX. 1 RI=Refractivity intercept (7lr d4). By calculation from rcfractlvity intercept. TABLE IX 25 Fractional distillation of composite sample obtained from TABLE V triple chromatogram Chromatographic fractionation of the coal tar naphtha Boiling Percent fraction Over silica gel Fraction Pgigtp Wt., g. Wt. 71,," 01" RI b [800 g. fraction sample] 9.1 5.9 1.55412 0.9030 1 0723 Volume Percent 49.4 32.5 1. 57147 0.9905 1 0762 Cut No. 0. 111 45.5 29.9 1.57358 0.9012 1 0780 25.1 10.4 1. 57360 0. 9913 1 0780 Cut Accum. 2. 8 1. 3

6.1 22. 9 1. 5155 0. 8988 1. 0661 9 Boiling points calculated to 760 mm. pressure. 6.7 29. 6 1. 5293 0 9194 1.0696 b Reiractivity intercept. 10.3 39.9 1.5380 0. 9344 1.0708 18. 7 58. 0 1. 5458 0. 947g 1. 0722 40 Fractions 4 and 5 are essentially pure indene and account 12.5 71.1 1.5558 0.904 1.0733 1M 9M M626 W060 W596 for 40% of the indene 1n the onglnal naphtha. Frac- 1. 5013 1.0222 1.0502 t1on 3 1s greater than 95% punty. These three fract1ons represent about 60% of the indene in the original naph- Includes bottoms from chromatogram in Table V. tha and are for all practical purposes pure indene. Refmmvlty intercept The advantages of the chromatographic separation followed by fractional distillation are shown in summary Fractions 5 through 8 from the run described in Table Table X,

V, and 13 through 17 from the run described in Table TABLE X VI were combined and subjected to a second chromato- 7 graphic separation. The results are shown in Table VII. Napmha A TABLE VII ery, Purity Percent Rechromatographic fractionation of composite fraction Charge 100 I140 Product: Vol. Percent Fract- Dism g C N 0!- 26 1b I e e r0- Single Ghromatogram 51 3 76 R g; 5 3? Single Ohrornatogram+Distillatiou. 00 95 Frae- Orig- Percent Double Chromntogrnm 28-3 23 mm Triple Chromatogram 05 Triple Chromatogram-I-Distillatlon 60 100 e l a 3.1 1.9 -1. 5428 EXAMPLE HI 8:3 T 3:3 Another naphtha containing 68% indene was subjected 14.3 8.9 1.5079 to a smgle chromatographic fractionation. A fraction -32 3:3 1:223: representing 72.5% of the naphtha and containing about 0.5 4.1 75% indene was recovered. This was fractionally dist1lled to produce a fraction amounting to 46.8% of the :Recovered from alcohol eluted material. 70 on'ginal naphtha and containing about 97% indene. Refrfrcflnty intercept Another fraction representing 8% of. the naphtha con- 1 0 tained 93% indene. Together these represented a total Fractions A to A, from Table VII were then comrecovery of 79% of the indene of greater than 95% bined and subjected to a third chromatographic separapurity. tion. The results of this are shown in Table VIII. 5 Rechromatographing the non-hydrocarbon fraction followed by fractional distillation of the two fractions obtained yielded 1.8% cou'm-arone, 4.4% methyl coumarone and 1.4% benzonitrile, based on the original naphtha.

EXAMPLE IV 94% were obtained. The three combined represented a 90% recovery of indene of greater than 95% purity. The non-hydrocarbon fraction was subjected to a sec ond chromatographic fractionation. Two of the fractions obtained were fractionally -distilled yielding 3.5% coumarone, 0.5% methyl coumarone and 0.3% benzoni-trile. These values are calculated on the original naphtha.

One of the fractions of this naphtha from the chromatographic fractionation contained styrene and substituted styrenes in rather high concentration. These amounted to 6.1% and 4.1% respectively, of the original naphtha. The other naphthas used contained no styrene.

Similar results have been obtained using activated alumina. Activated alumina adsorbs the nitriles more strongly than does silica gel. Consequently it may be desirable in some instances to first pass the naphtha through activated alumina to concentrate the nitriles and other non-hydrocarbon components. In this case a relatively high liquid to adsorbent ratio is used. The exact ratio will vary depending on the proportions of the non-hydrocarbons present, and upon the degree of separation desired. After the treatment With alumina, the chromatographic fractionation, as previously described, can be carried out using either silica gel, activated alumina or other suitable adsorbent. The preliminary treatment can also be carried out using silica gel in a like manner.

We claim as our invention:

1. A process for separating indene of high purity from a naphtha fraction boiling predominantly in the range of 160-200" C. and composed essentially of a complex mixture of aromatic hydrocarbons including methyl benzene-s, indane, and other aromatic hydrocarbons normally present in coal tar naphtha fractions of this boiling range, and polymerizable constituents other than indene, in which indene is the predominant single hydrocarbon and is present in at least about 35% by volume of the naphtha fraction, which comprises contacting said naphtha fraction with an adsorbent selected from the group consisting of silica gel, activated alumina, and activated carbon in an adsorption zone, selectively adsorbing an indene-rich fraction, desorbing the adsorbed material from the adsorbent, and recovering a fraction of relatively low indene content and a fraction rich in indene.

2. A process for separating indene of high purity from a naphtha fraction boiling predominantly in the range of 160-200 C. and composed essentiallyof a complex mixture of aromatic hydrocarbons including methyl benzenes, indane, and other aromatic hydrocarhons normally present in coal tar naphtha fractions of this boiling range, and polymeriza'ole constituents other than indene, in which indene is the predominant single hydrocarbon and is present in at least about 35% by volume of the naphtha fraction, which comprises contacting said naphtha fraction with an adsorbent selected from the group consisting of silica gel, activated alumina, and activated carbon in an adsorption zone, selectively adsorbing an 'indene-rich fraction, desorbing the ad sorbed' material from the adsorbent, recovering a frat:- tion or" relatively low ind-one content and a fraction rich in indene, and thereafter fractionaily distilling said indene-rich fraction and recovering a product of increased indene content, said product containing the major portion of the indene contained in the original naphtha fraction.

3. The process of claim 2 wherein the indene content of said product is greater than about 95% by weight.

4. The process of claim 1 wherein the indene-rich fraction is subjected to a second adsorption step with said adsorbent, the adsorbed material is desorbed, a fraction.

fractio'nal distillation and a product of greater indene content is recovered. I

6. The process of claim '1 wherein a first fraction of low indene content is recovered, a second fraction of 1 intermediate indene content is recovered, and a third fraction of high indene content is recovered, the fraction of intermediate indene content is subjected to a second adsorption step, the adsorbed material from the second adsorption step is desorbed, a fraction of low ind'ene content and another fraction of high indene conand the high indene content'iraction from said second tent is recovered as a product.

7. The process of claim 7 wherein said third fraction adsorption step are subjected to fractional distillation, and a product of enhanced indene content is recovered from said distillation step.

References Cited in the file of this patent UNITED STATES PATENTS 2,395,491 Mavity Feb. 26, 1946 2,398,101 Lipkin Apr. 9, 1946 2,509,486 Danforth May 30, 1950 2,518,236 Hirschler Aug. 8, 1950 2,756,197 Thorpe et. a1. July 24, 1956 2,763,701 Hoffman et a1. Sept. 18, 1956 2,768,221 Findlay Oct. 23, 1956 OTHER REFERENCES I Mair et al.: J. Research, Nat. But. of Standards, volume 32 (1944), paper No. 1583, pages -183 (page 183 only needed).

Karren: Organic Chemistry, 2nd ed., 1946, pages I 

1. A PROCESS FOR SEPARATING INDENE OF HIGH PURITY FROM A NAPHTHA FRACTION BOILING PREDOMINANTLY IN THE RANGE OF 160-200*C. AND COMPOSED ESSENTIALLY OF A COMPLEX MIXTURE OF AROMATIC HYDROCARBONS INDLUDING METHYL BENZENES, INDANE, AND OTHER AROMATIC HYDROCARBONS NORMALLY PRESENT IN COAL TAR NAPHTHA FRACTIONS OF THIS BOILING RANGE, AND POLYMERIZABLE CONSTITUENTS OTHER THAN INDENE, IN WHICH INDENE IS THE PREDOMINANT SINGLE HYDROCARBON AND IS PRESENT IN A LEAST ABOUT 35% BY VOLUME OF THE NAPHTHA FRACTION, WHICH COMPRISES CONTACTING SAID NAPHTHA FRACTION WITH AN ADSORBENT SELECTED FROM THE GROUP CONSISTING OF SILICA GEL, ACTIVATED ALUMINA, AND ACTIVATED CARBON IN A ADSORPTION ZONE, SELECTIVELY ADSORBING AN INDENE-RICH FRACTION, DESORBING THE ADSORBED MATERIAL FROM THE ADSORBENT, AND RECOVERING A FRACTION OF RELATIVELY LOW INDENE CONTENT AND A FRACTION RICH IN INDENE. 